sched_ext: Maintain an online cid mask in the scheduler arenagrafted

Schedulers on the default cid mapping treat [0, nr_online_cids) as the
online set and restart on hotplug. Schedulers that install their own mapping
with scx_bpf_cid_override() have no way to learn which cids are online: the
count no longer identifies members and the CPU-form cpumask is unusable from
cid programs. This is an obvious hole in the cid API.

Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's
arena, allocated alongside the per-CPU scratch masks and populated after the
cid mapping is finalized and before ops.init(), for child schedulers too.
The pointer stays valid through ops.exit() with no reference to take. It is
the arena offset as a void pointer, the same form struct_ops arena arguments
arrive in. The verifier types the void return as a scalar for the program's
arena cast.

The mask follows the SCX hotplug notifications: seeded from cpu_active_mask
and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask
only inside a hotplug transition. Updates walk the scheduler list under the
lock that also serializes unlinking. Reads are live, not atomic snapshots.
Root initialization excludes hotplug.

v2: Reworded the getter kerneldoc (Andrea Righi).

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

1 files changed, 321 insertions, 0 deletions

diff --git a/arch/m68k/atari/time.c b/arch/m68k/atari/time.c
new file mode 100644
index 000000000..3453c6dc6
--- /dev/null
+++ b/arch/m68k/atari/time.c
@@ -0,0 +1,321 @@
+/*
+ * linux/arch/m68k/atari/time.c
+ *
+ * Atari time and real time clock stuff
+ *
+ * Assembled of parts of former atari/config.c 97-12-18 by Roman Hodek
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file COPYING in the main directory of this archive
+ * for more details.
+ */
+
+#include <linux/types.h>
+#include <linux/mc146818rtc.h>
+#include <linux/interrupt.h>
+#include <linux/init.h>
+#include <linux/rtc.h>
+#include <linux/bcd.h>
+#include <linux/clocksource.h>
+#include <linux/delay.h>
+#include <linux/export.h>
+
+#include <asm/atariints.h>
+#include <asm/machdep.h>
+
+#include "atari.h"
+
+DEFINE_SPINLOCK(rtc_lock);
+EXPORT_SYMBOL_GPL(rtc_lock);
+
+static u64 atari_read_clk(struct clocksource *cs);
+
+static struct clocksource atari_clk = {
+	.name   = "mfp",
+	.rating = 100,
+	.read   = atari_read_clk,
+	.mask   = CLOCKSOURCE_MASK(32),
+	.flags  = CLOCK_SOURCE_IS_CONTINUOUS,
+};
+
+static u32 clk_total;
+static u8 last_timer_count;
+
+static irqreturn_t mfp_timer_c_handler(int irq, void *dev_id)
+{
+	unsigned long flags;
+
+	local_irq_save(flags);
+	do {
+		last_timer_count = st_mfp.tim_dt_c;
+	} while (last_timer_count == 1);
+	clk_total += INT_TICKS;
+	legacy_timer_tick(1);
+	timer_heartbeat();
+	local_irq_restore(flags);
+
+	return IRQ_HANDLED;
+}
+
+void __init
+atari_sched_init(void)
+{
+    /* set Timer C data Register */
+    st_mfp.tim_dt_c = INT_TICKS;
+    /* start timer C, div = 1:100 */
+    st_mfp.tim_ct_cd = (st_mfp.tim_ct_cd & 15) | 0x60;
+    /* install interrupt service routine for MFP Timer C */
+    if (request_irq(IRQ_MFP_TIMC, mfp_timer_c_handler, IRQF_TIMER, "timer",
+                    NULL))
+	pr_err("Couldn't register timer interrupt\n");
+
+    clocksource_register_hz(&atari_clk, INT_CLK);
+}
+
+/* ++andreas: gettimeoffset fixed to check for pending interrupt */
+
+static u64 atari_read_clk(struct clocksource *cs)
+{
+	unsigned long flags;
+	u8 count;
+	u32 ticks;
+
+	local_irq_save(flags);
+	/* Ensure that the count is monotonically decreasing, even though
+	 * the result may briefly stop changing after counter wrap-around.
+	 */
+	count = min(st_mfp.tim_dt_c, last_timer_count);
+	last_timer_count = count;
+
+	ticks = INT_TICKS - count;
+	ticks += clk_total;
+	local_irq_restore(flags);
+
+	return ticks;
+}
+
+
+static void mste_read(struct MSTE_RTC *val)
+{
+#define COPY(v) val->v=(mste_rtc.v & 0xf)
+	do {
+		COPY(sec_ones) ; COPY(sec_tens) ; COPY(min_ones) ;
+		COPY(min_tens) ; COPY(hr_ones) ; COPY(hr_tens) ;
+		COPY(weekday) ; COPY(day_ones) ; COPY(day_tens) ;
+		COPY(mon_ones) ; COPY(mon_tens) ; COPY(year_ones) ;
+		COPY(year_tens) ;
+	/* prevent from reading the clock while it changed */
+	} while (val->sec_ones != (mste_rtc.sec_ones & 0xf));
+#undef COPY
+}
+
+static void mste_write(struct MSTE_RTC *val)
+{
+#define COPY(v) mste_rtc.v=val->v
+	do {
+		COPY(sec_ones) ; COPY(sec_tens) ; COPY(min_ones) ;
+		COPY(min_tens) ; COPY(hr_ones) ; COPY(hr_tens) ;
+		COPY(weekday) ; COPY(day_ones) ; COPY(day_tens) ;
+		COPY(mon_ones) ; COPY(mon_tens) ; COPY(year_ones) ;
+		COPY(year_tens) ;
+	/* prevent from writing the clock while it changed */
+	} while (val->sec_ones != (mste_rtc.sec_ones & 0xf));
+#undef COPY
+}
+
+#define	RTC_READ(reg)				\
+    ({	unsigned char	__val;			\
+		(void) atari_writeb(reg,&tt_rtc.regsel);	\
+		__val = tt_rtc.data;		\
+		__val;				\
+	})
+
+#define	RTC_WRITE(reg,val)			\
+    do {					\
+		atari_writeb(reg,&tt_rtc.regsel);	\
+		tt_rtc.data = (val);		\
+	} while(0)
+
+
+#define HWCLK_POLL_INTERVAL	5
+
+int atari_mste_hwclk( int op, struct rtc_time *t )
+{
+    int hour, year;
+    int hr24=0;
+    struct MSTE_RTC val;
+
+    mste_rtc.mode=(mste_rtc.mode | 1);
+    hr24=mste_rtc.mon_tens & 1;
+    mste_rtc.mode=(mste_rtc.mode & ~1);
+
+    if (op) {
+        /* write: prepare values */
+
+        val.sec_ones = t->tm_sec % 10;
+        val.sec_tens = t->tm_sec / 10;
+        val.min_ones = t->tm_min % 10;
+        val.min_tens = t->tm_min / 10;
+        hour = t->tm_hour;
+        if (!hr24) {
+	    if (hour > 11)
+		hour += 20 - 12;
+	    if (hour == 0 || hour == 20)
+		hour += 12;
+        }
+        val.hr_ones = hour % 10;
+        val.hr_tens = hour / 10;
+        val.day_ones = t->tm_mday % 10;
+        val.day_tens = t->tm_mday / 10;
+        val.mon_ones = (t->tm_mon+1) % 10;
+        val.mon_tens = (t->tm_mon+1) / 10;
+        year = t->tm_year - 80;
+        val.year_ones = year % 10;
+        val.year_tens = year / 10;
+        val.weekday = t->tm_wday;
+        mste_write(&val);
+        mste_rtc.mode=(mste_rtc.mode | 1);
+        val.year_ones = (year % 4);	/* leap year register */
+        mste_rtc.mode=(mste_rtc.mode & ~1);
+    }
+    else {
+        mste_read(&val);
+        t->tm_sec = val.sec_ones + val.sec_tens * 10;
+        t->tm_min = val.min_ones + val.min_tens * 10;
+        hour = val.hr_ones + val.hr_tens * 10;
+	if (!hr24) {
+	    if (hour == 12 || hour == 12 + 20)
+		hour -= 12;
+	    if (hour >= 20)
+                hour += 12 - 20;
+        }
+	t->tm_hour = hour;
+	t->tm_mday = val.day_ones + val.day_tens * 10;
+        t->tm_mon  = val.mon_ones + val.mon_tens * 10 - 1;
+        t->tm_year = val.year_ones + val.year_tens * 10 + 80;
+        t->tm_wday = val.weekday;
+    }
+    return 0;
+}
+
+int atari_tt_hwclk( int op, struct rtc_time *t )
+{
+    int sec=0, min=0, hour=0, day=0, mon=0, year=0, wday=0;
+    unsigned long	flags;
+    unsigned char	ctrl;
+    int pm = 0;
+
+    ctrl = RTC_READ(RTC_CONTROL); /* control registers are
+                                   * independent from the UIP */
+
+    if (op) {
+        /* write: prepare values */
+
+        sec  = t->tm_sec;
+        min  = t->tm_min;
+        hour = t->tm_hour;
+        day  = t->tm_mday;
+        mon  = t->tm_mon + 1;
+        year = t->tm_year - atari_rtc_year_offset;
+        wday = t->tm_wday + (t->tm_wday >= 0);
+
+        if (!(ctrl & RTC_24H)) {
+	    if (hour > 11) {
+		pm = 0x80;
+		if (hour != 12)
+		    hour -= 12;
+	    }
+	    else if (hour == 0)
+		hour = 12;
+        }
+
+        if (!(ctrl & RTC_DM_BINARY)) {
+	    sec = bin2bcd(sec);
+	    min = bin2bcd(min);
+	    hour = bin2bcd(hour);
+	    day = bin2bcd(day);
+	    mon = bin2bcd(mon);
+	    year = bin2bcd(year);
+	    if (wday >= 0)
+		wday = bin2bcd(wday);
+        }
+    }
+
+    /* Reading/writing the clock registers is a bit critical due to
+     * the regular update cycle of the RTC. While an update is in
+     * progress, registers 0..9 shouldn't be touched.
+     * The problem is solved like that: If an update is currently in
+     * progress (the UIP bit is set), the process sleeps for a while
+     * (50ms). This really should be enough, since the update cycle
+     * normally needs 2 ms.
+     * If the UIP bit reads as 0, we have at least 244 usecs until the
+     * update starts. This should be enough... But to be sure,
+     * additionally the RTC_SET bit is set to prevent an update cycle.
+     */
+
+    while( RTC_READ(RTC_FREQ_SELECT) & RTC_UIP ) {
+	if (in_atomic() || irqs_disabled())
+	    mdelay(1);
+	else
+	    schedule_timeout_interruptible(HWCLK_POLL_INTERVAL);
+    }
+
+    local_irq_save(flags);
+    RTC_WRITE( RTC_CONTROL, ctrl | RTC_SET );
+    if (!op) {
+        sec  = RTC_READ( RTC_SECONDS );
+        min  = RTC_READ( RTC_MINUTES );
+        hour = RTC_READ( RTC_HOURS );
+        day  = RTC_READ( RTC_DAY_OF_MONTH );
+        mon  = RTC_READ( RTC_MONTH );
+        year = RTC_READ( RTC_YEAR );
+        wday = RTC_READ( RTC_DAY_OF_WEEK );
+    }
+    else {
+        RTC_WRITE( RTC_SECONDS, sec );
+        RTC_WRITE( RTC_MINUTES, min );
+        RTC_WRITE( RTC_HOURS, hour + pm);
+        RTC_WRITE( RTC_DAY_OF_MONTH, day );
+        RTC_WRITE( RTC_MONTH, mon );
+        RTC_WRITE( RTC_YEAR, year );
+        if (wday >= 0) RTC_WRITE( RTC_DAY_OF_WEEK, wday );
+    }
+    RTC_WRITE( RTC_CONTROL, ctrl & ~RTC_SET );
+    local_irq_restore(flags);
+
+    if (!op) {
+        /* read: adjust values */
+
+        if (hour & 0x80) {
+	    hour &= ~0x80;
+	    pm = 1;
+	}
+
+	if (!(ctrl & RTC_DM_BINARY)) {
+	    sec = bcd2bin(sec);
+	    min = bcd2bin(min);
+	    hour = bcd2bin(hour);
+	    day = bcd2bin(day);
+	    mon = bcd2bin(mon);
+	    year = bcd2bin(year);
+	    wday = bcd2bin(wday);
+        }
+
+        if (!(ctrl & RTC_24H)) {
+	    if (!pm && hour == 12)
+		hour = 0;
+	    else if (pm && hour != 12)
+		hour += 12;
+        }
+
+        t->tm_sec  = sec;
+        t->tm_min  = min;
+        t->tm_hour = hour;
+        t->tm_mday = day;
+        t->tm_mon  = mon - 1;
+        t->tm_year = year + atari_rtc_year_offset;
+        t->tm_wday = wday - 1;
+    }
+
+    return( 0 );
+}